What Is A Lethal Dose Of Benadryl (Diphenhydramine)?

Benadryl, known by its medical name as diphenhydramine, is an antihistamine used to treat allergic reactions and seasonal allergies. Ingredients vary depending on the type of Benadryl medication being used, but all Benadryl medications contain diphenhydramine.

In recent years there has been an uptick in individuals abusing Benadryl in order to get high. This requires taking a dosage much greater than recommended by the prescribing guidelines. Individuals may crush and snort Benadryl to feel the effects faster.

A fatal dose of diphenhydramine is about 20 to 40 milligrams per kilogram (mg/kg).

Learn more about the fatal doses of commonly abused drugs.

What To Know About A Lethal Dose Of Benadryl (Diphenhydramine)

The lethal dose of diphenhydramine depends on a few factors, such as the condition it’s being used to treat and the person’s age.

The lethal dose of diphenhydramine has been estimated to be 20 to 40 mg per 1 kg for adults. For children, the lethal dose is 500 milligrams (mg).

According to a 2026 report from the American Association of Poison Control Centers (AAPCC), most intoxication and overdose cases occur in children six years old and under. Children are at a higher risk of overdose than adults because they are more sensitive to the effects of antihistamines.

How Likely Is Overdose On Benadryl (Diphenhydramine)?

Studies have found that diphenhydramine toxicity is dose-dependent, meaning the dangerous effects of the drug increase as the amount taken increases, and taking too much diphenhydramine either intentionally or accidentally can potentially be lethal.

While there have been documented fatal cases over the last few decades, death resulting from diphenhydramine overdose is not common, especially when people receive prompt medical treatment after recognizing the symptoms of poisoning.

How Does Benadryl (Diphenhydramine) Overdose Happen?

The lethal dose of 20 to 40 mg/kg is three to five times the recommended daily dose, so an overdose on Benadryl is intentional in most cases. A person might intentionally ingest a large amount of Benadryl in an act of suicide or self-harm. A study surveying drug-related deaths in the U.S. from 2011 to 2016 found that diphenhydramine is one of the top four most frequently mentioned drugs in suicide overdose cases.

Others intentionally overdose to feel a high, although euphoria does not usually occur after taking Benadryl. In accidental cases of overdose, Benadryl is usually combined with other medications and substances.

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Signs And Symptoms Of Benadryl Overdose

Benadryl overdose can cause a wide range of symptoms that vary from mild discomfort to life-threatening medical emergencies. These warning signs may start as minor symptoms and can quickly progress to serious complications.

Common signs of Benadryl overdose include:

• Dry Mouth, Eyes, and Red Skin: the body loses its ability to produce normal moisture, leading to uncomfortable dryness throughout the body
• Blurred Vision and Ringing in the Ears: sensory problems that make it difficult to see clearly or hear normally
• Drowsiness and Heavy Sedation: extreme sleepiness that can progress to being unable to stay awake or respond normally
• Inability to Urinate: the bladder muscles become affected, making it difficult or impossible to empty the bladder
• Rapid Heartbeat or Cardiac Arrest: the heart may race dangerously fast or, in severe cases, stop beating altogether
• Hallucinations and Confusion: seeing or hearing things that aren’t real, along with severe mental confusion
• Seizures and Unconsciousness: uncontrolled muscle spasms and loss of consciousness that can lead to coma
• Depression and Liver Damage: mood changes and potentially permanent damage to vital organs

A person who overdoses on Benadryl can develop serious anticholinergic symptoms, which happen when the drug blocks important brain chemicals that control basic body functions.

These overdoses are particularly dangerous because they can cause seizures, coma, and other life-threatening complications that require emergency medical treatment.

Pregnant women face additional risks, as Benadryl overdose can cause serious complications for both mother and baby.

What To Do If Someone Has Overdosed On Benadryl (Diphenhydramine)

If you or a loved one are showing signs of a Benadryl overdose, seek emergency medical help immediately by calling 911.

Don’t wait to see if symptoms get worse or try to treat the overdose at home, as Benadryl poisoning can quickly become life-threatening and requires medical care. Emergency responders and hospital staff have the proper medications and equipment needed to reverse the effects of the overdose.

You can also contact your local poison control center for immediate guidance on what to do next by calling the national poison control hotline at 1-800-222-1222.

While a diphenhydramine overdose is not always fatal, especially when treated quickly, it’s important to remember that every overdose situation is potentially dangerous and should be treated as a medical emergency. Poison control experts can provide specific instructions while you wait for emergency services.

Reach out to the Substance Abuse and Mental Health Services Administration (SAMHSA) for more information about substance use disorders and recovery options.

Written by the Addiction Resource Editorial Staff